1. Field of the Invention
The invention relates to an optical microwave source structured as a multi-section semiconductor laser the sections of which are structured to be separately electrically controllable.
2. The Prior Art.
Various types and arrangements of such multi-section semiconductor lasers have been described in the prior art.
A self-modulated laser with DFB/phase/DFB sections in which the second DFB (distributed feedback) section structured as a passive reflector and thus makes dispersive Q switching possible, has been described in IEEE Journal of Quantum Electronics, Vol. 33, No. 2, February 1997, pp. 211-218 in the paper “Dispersive Self-Q-Switching in Self-Pulsating DFB Lasers” by B. Sartorius, M. Moehrle, S. Reichenbacher, H. Preier, H.-J. Wuensche, U. Bandelow and in German patent specification DE 195 13 198. The laser is limited to frequencies in the range of the resonant frequency <20 GHz. The microwave frequency can be tuned within the confines of tuning the resonant frequency by the current in the actively driven DFB section.
European patent specification EP 1.087,478 describes a self-modulated laser with sections DFB/phase/DFB or DFB/DFB wherein both DFB sections are actively driven. The coupling of the two DFB modes in the complete resonator results in a microwave which is proportional to the spacing of the DFB modes of the different DFB sections. The limit of the upper cutoff frequency is determined by the distance of the modes of the two lasers from each other, rather than by their resonant frequencies. Because of the complexity of the structural components including two DFB lasers, the approach necessitates highly precise technology to ensure the fabrication of identical structural elements. Because of unavoidable accidental parameters such as, for instance, the phase relationship between lattices, the yield is very low and is further reduced by a lack of tunability.
In their paper “High-Frequency Oscillation and Self-Mode Locking in Short External-Cavity Laser Diodes” in IEEE Journal of Quantum Electronics, Vol. 30, No. 7, July 1994, pp. 1553-1561 Tager and Petermann have proposed a DFB laser with an integrated passive cavity. This type of structural component avoids the technological problems of the approach described supra. In this structure, the upper microwave frequency is significantly reduced by the optical losses in the integrated passive cavity and is limited to 30 GHz.
The solutions for sources of optical microwaves mentioned in the prior art are either limited as regards their frequency or they are technologically very complex.